Variator fault detection system

ABSTRACT

A variator fault detection system for a continuously variable transmission is incorporated into a hydraulic control circuit that controls fluid pressure applied to a variator of the continuously variable transmission. The hydraulic control circuit for the variator includes a number of electrically-controlled shift valves and pressure control valves. Sensing devices are multiplexed to these valves to detect a number of different possible fault states relating to the variator shift valves and the variator pressure control valves.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 12/943,386, entitled “VARIATOR FAULT DETECTION SYSTEM,” which wasfiled on Nov. 10, 2010, and which claims priority to U.S. ProvisionalPatent Application Serial No. 61/286,984, which was filed on Dec. 16,2009, the entirety of both of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to vehicle transmissions thathave a ratio varying unit, and more particularly, to a variator faultdetection system for a transmission having a ratio varying unit of thefull toroidal type.

BACKGROUND

In some vehicle transmissions, a ratio varying unit (“variator”) is usedto provide a continuous variation of transmission ratio rather than aseries of predetermined ratios. These transmissions may be referred toas continuously variable transmissions, infinitely variabletransmissions, toroidal transmissions, continuously variabletransmissions of the full toroidal race-rolling traction type, orsimilar terminology. In such transmissions, the variator is coupledbetween the transmission input and the transmission output via gearingand one or more clutches. In the variator, torque is transmitted by thefrictional engagement of variator disks and rollers separated by atraction fluid.

The variator torque is controlled by a hydraulic circuit, which includeshydraulic actuators (i.e., pistons) that apply an adjustable force tothe rollers. The force applied by the hydraulic actuator is balanced bya reaction force resulting from the torques transmitted between thesurfaces of the variator disks and the rollers. The end result is thatin use, each roller moves and precesses to the location and tilt anglerequired to transmit a torque determined by the force applied by thehydraulic actuators. A difference in the forces applied to the rollerschanges the rollers' tilt angle and thus, the variator ratio. A changein the rollers' tilt angle thus results not only in a net torque at thetransmission output but could also result in a change in torquedirection. The direction of the torque output determines whether thetorque application is positive or negative.

SUMMARY

According to one aspect of this disclosure, a variator fault detectioncircuit, comprising a first shift valve movable from a first position toa second position axially spaced from the first position in a firstvalve chamber of a hydraulic control circuit for a continuously variabletransmission. The first shift valve has a first port in fluidcommunication with a variator of the continuously variable transmissionand a second port axially spaced from the first port. The circuit alsoincludes a second shift valve movable from a first position to a secondposition axially spaced from the first position in a second valvechamber of the hydraulic control circuit of the continuously variabletransmission. The second shift valve has a first port in fluidcommunication with the variator of the continuously variabletransmission and a second port axially spaced from the first port. Thecircuit also includes a first pressure switch coupled to the second portof the first shift valve, a second pressure switch coupled to the secondport of the second shift valve, a first electro-hydraulic actuatorcoupled to the first shift valve, and a second electro-hydraulicactuator coupled to the second shift valve.

In some embodiments, the first position of the first shift valve is adestroked position and the second position of the first shift valve is astroked position. Also in some embodiments, the first position of thesecond shift valve is a destroked position and the second position ofthe second shift valve is a stroked position.

The variator fault detection circuit may include a first trim valveoperable to output variable fluid pressure, where the first trim valveis fluidly coupled to the first port of the first shift valve when thefirst shift valve is in the first position, and the first trim valve isdisconnected from the first port of the first shift valve when the firstshift valve is in the second position.

The variator fault detection circuit may include a second trim valveoperable to output variable fluid pressure, wherein the second trimvalve is fluidly coupled to the first port of the second shift valvewhen the second shift valve is in the first position, and the secondtrim valve is disconnected from the first port of the second trim valvewhen the second shift valve is in the second position.

According to another aspect of this disclosure, a shift valve faultdetection method executable by an electronic control unit using avariator fault detection circuit includes detecting a status of thefirst pressure switch, detecting a status of the first electro-hydraulicactuator, and determining whether a fault has occurred at the firstshift valve based on the status of the first pressure switch and thestatus of the first electro-hydraulic actuator.

The shift valve fault detection method may include initiating a failurerecovery action in response to determining that a fault has occurred atthe first shift valve. The shift valve fault detection method mayinclude detecting a status of the second pressure switch, detecting astatus of the second electro-hydraulic actuator, and determining whethera fault has occurred at the second shift valve based on the status ofthe second pressure switch and the status of the secondelectro-hydraulic actuator.

According to yet another aspect of this disclosure, a variator faultdetection circuit includes a first shift valve movable from a firstposition to a second position axially spaced from the first position ina first valve chamber of a hydraulic control circuit for a continuouslyvariable transmission. The first shift valve has a first port in fluidcommunication with a variator of the continuously variable transmissionand a second port axially spaced from the first port. The variator faultdetection circuit also includes a second shift valve movable from afirst position to a second position axially spaced from the firstposition in a second valve chamber of the hydraulic control circuit ofthe continuously variable transmission. The second shift valve has afirst port in fluid communication with the variator of the continuouslyvariable transmission and a second port axially spaced from the firstport. The circuit also includes a first pressure switch coupled to thesecond port of the first shift valve, a second pressure switch coupledto the second port of the second shift valve, and a variator fault valveselectively coupled to the second port of the first shift valve andselectively coupled to the second port of the second shift valve.

The variator fault valve may have a first position and a second positionaxially spaced from the first position, where the variator fault valveoutputs fluid pressure to at least one of the second port of the firstshift valve and the second port of the second shift valve when thevariator fault valve is in the second position. The variator fault valvemay only output fluid pressure to the second port of the first shiftvalve when the first shift valve is in the first position and thevariator fault valve is in the second position. The variator fault valvemay only output fluid pressure to the second port of the second shiftvalve when the second shift valve is in the first position and thevariator fault valve is in the second position.

According to another aspect of this disclosure, a variator faultdetection method executable by an electronic control unit using avariator fault detection circuit includes detecting a status of thefirst pressure switch, detecting a status of the second pressure switch,and determining whether a variator fault has occurred based on thestatus of the first pressure switch and the status of the secondpressure switch. The determining step of the method may includedetermining whether the first and second pressure switches are bothactuated. The variator fault detection method may include initiating afault recovery action if the status of the first pressure switch isactuated and the status of the second pressure switch is actuated.

According to a further aspect of this disclosure, a variator trim systemfault detection circuit includes a first shift valve movable from afirst position to a second position axially spaced from the firstposition in a first valve chamber of a hydraulic control circuit for acontinuously variable transmission. The first shift valve has a firstport in fluid communication with the variator of a continuously variabletransmission and a second port axially spaced from the first port. Thevariator trim system fault detection circuit also includes a secondshift valve movable from a first position to a second position axiallyspaced from the first position in a second valve chamber of thehydraulic control circuit of the continuously variable transmission. Thesecond shift valve has a first port in fluid communication with thevariator of the continuously variable transmission and a second portaxially spaced from the first port.

The variator trim system fault detection circuit also includes a firsttrim valve operable to output variable fluid pressure, where the firsttrim valve is fluidly coupled to the first port of the first shift valvewhen the first shift valve is in the first position, and the first trimvalve is disconnected from the first port of the first shift valve whenthe first shift valve is in the second position.

The variator trim system fault detection circuit also includes a secondtrim valve operable to output variable fluid pressure, where the secondtrim valve is fluidly coupled to the first port of the second shiftvalve when the second shift valve is in the first position, and thesecond trim valve is disconnected from the first port of the second trimvalve when the second shift valve is in the second position.

The variator trim system fault detection circuit also includes a firstpressure switch coupled to the second port of the first shift valve, asecond pressure switch coupled to the second port of the second shiftvalve, a first electro-hydraulic actuator coupled to the first shiftvalve, a second electro-hydraulic actuator coupled to the second shiftvalve, and a variator fault valve selectively coupled to the second portof the first shift valve and selectively coupled to the second port ofthe second shift valve.

Each of the first and second shift valves may have a valve head and aspring pocket axially spaced from the valve head, where the variatortrim system fault detection circuit includes a first passage fluidlycoupling the valve head of the first shift valve to the spring pocket ofthe second shift valve. The variator trim system fault detection circuitmay include a second passage fluidly coupling the valve head of thesecond shift valve to the spring pocket of the first shift valve.

According to another aspect of this disclosure, a variator trim systemfault detection method executable by an electronic control unit using avariator trim system fault detection circuit includes detecting a statusof the first pressure switch, detecting a status of the second pressureswitch, detecting a status of the second electro-hydraulic actuator, anddetermining whether a fault has occurred at the first trim valve basedon the status of the first pressure switch, the status of the secondpressure switch, and the status of the second electro-hydraulicactuator.

The variator trim system fault detection method may include initiating afailure recovery action in response to determining that a fault hasoccurred at the first trim valve. The variator trim system faultdetection method may include detecting a status of the firstelectro-hydraulic actuator, and determining whether a fault has occurredat the second shift valve based on the status of the first pressureswitch, the status of the second pressure switch, and the status of thefirst electro-hydraulic actuator.

According to yet another aspect of this disclosure, a variator controlcircuit includes a plurality of variator control devices in fluidcommunication with each other and with a variator of a continuouslyvariable transmission, and a maximum of two sensing devices configuredto detect faults occurring in any one of the plurality of variatorcontrol devices.

In the variator control circuit, the plurality of variator controldevices may include a pair of shift valves and a plurality of trimvalves, where each of the shift valves has a first port and a secondport axially spaced from the first port, and each of the trim valves isselectively coupled to the first port of a shift valve, and each of thesensing devices is coupled to the second port of one of the shiftvalves. The variator control circuit may include a variator fault valveselectively coupled to the second port of the shift valves. In thevariator control circuit, each of the shift valves may have a valve headand a spring pocket, and the circuit may include a first passage fluidlycoupling the valve head of the first shift valve to the spring pocket ofthe second shift valve and a second passage fluidly coupling the valvehead of the second shift valve to the spring pocket of the first shiftvalve.

Patentable subject matter may include one or more features orcombinations of features shown or described anywhere in this disclosureincluding the written description, drawings, and claims

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description refers to the following figures in which:

FIG. 1A is a schematic showing a variator fault detection system in thecontext of an exemplary vehicle transmission;

FIG. 1B is a partially schematic simplified side view of a portion of avariator suitable for use in the transmission of FIG. 1A;

FIG. 1C is a simplified top view of the variator of FIG. 1B, withportions omitted for clarity;

FIG. 2 is a schematic showing the variator fault detection system ofFIG. 1A in a hydraulic control circuit for the transmission of FIG. 1A;and

FIGS. 3-6 are schematic representations of different states of thevariator fault detection system of FIG. 1A.

In figures that depict schematic illustrations, the components may notbe drawn to scale, and lines shown as connecting the various blocks andcomponents shown therein represent connections which, in practice, mayinclude one or more electrical, mechanical and/or fluid connections,passages, communication links, couplings or linkages, as will beunderstood by those skilled in the art and as described herein. Ingeneral, like structural elements on different figures refer toidentical or functionally similar structural elements, althoughreference numbers may be omitted from certain views of the drawings forease of illustration.

DETAILED DESCRIPTION

Aspects of this disclosure are described with reference to illustrativeembodiments shown in the accompanying drawings and described herein.While the disclosure refers to these illustrative embodiments, it shouldbe understood that the present invention as claimed is not limited tothe disclosed embodiments. For example, while certain aspects of thedisclosure are discussed herein in the context of a continuouslyvariable transmission, it will be understood by those skilled in the artthat aspects of the present disclosure are applicable to other types andconfigurations of transmissions.

Also, transmissions of the type discussed herein may be referred to by anumber of different terms, including continuously variabletransmissions, infinitely variable transmissions, toroidaltransmissions, continuously variable transmissions of the full toroidalrace-rolling traction type, or similar terminology. In this disclosure,for ease of discussion, the term “continuously variable transmission” isused to refer to any of those types of transmissions in which the ratiosmay be controlled by a ratio varying unit, alternatively or in additionto being controlled by a set of gears that provide fixed, steppedratios.

In FIG. 1A, a variator fault detection system 126 is shown in relationto other components of a vehicle power train. The variator faultdetection system 126 is used in a hydraulic control circuit 28 for atransmission 12. In the illustrations, the transmission 12 is atransmission having a ratio varying unit of the full toroidal tractiontype. Transmissions of this type are available from TorotrakDevelopment, Ltd. of Lancashire, United Kingdom, for example.

The transmission 12 is coupled to a transmission input shaft 18 toreceive torque output by a vehicle drive unit 10. The drive unit 10includes an internal combustion engine, such as a spark-ignited engineor diesel engine, an engine-electric motor combination, or the like.

The transmission 12 uses a ratio varying unit (“variator”) 24 to providea continuous variation of transmission ratio. The variator 24 is coupledbetween the transmission input shaft 18 and the transmission outputshaft 20 via gearing 22 and one or more clutches 26. The linkages 32,34, 36 are used to schematically represent mechanical connectionsbetween components of the transmission 12, as will be understood bythose skilled in the art. The linkage 36 is representative of a variatoroutput shaft.

FIGS. 1B and 1C illustrate components of the variator 24. Inside thevariator 24, there is a pair of disks 21, 23. The input disk 21 iscoupled to and driven by the transmission input shaft 18, while theoutput disk 23 is coupled to the variator output shaft 36. The spacebetween the inner surfaces 29, 31 of the disks 21, 23 forms a hollowdoughnut shape or ‘toroid.’ A number of rollers 25, 27 are positionedwithin the toroidal space defined by the surfaces 29, 31. The rollers25, 27 transmit drive from the input disk 21 to the output disk 23 via atraction fluid (not shown).

Each of the rollers 25, 27 is coupled to a hydraulic actuator 35 by acarriage 33. The hydraulic pressure in the actuators 35 is adjusted bythe variator control circuit 28 as described below with reference toFIG. 2. Varying the pressures in the actuators 35 changes the forceapplied by the actuators 35 to their respective rollers 25, 27, tocreate a range of torque within the variator 24. The rollers 25, 27 arecapable of translational motion and also rotate about a tilt axisrelative to the variator disks 21, 23. FIG. 1C shows an example of therollers 25, 27 positioned at a tilt angle relative to the surfaces 29,31, with the actuators 35 omitted for clarity.

In one illustrative implementation, the variator 24 includes two pairsof input and output disks 21, 23, and there are three rollers positionedin the toroidal space defined by the disks of each pair, for a total ofsix rollers. Each roller is coupled to a hydraulic actuator 35, for atotal of six hydraulic actuators. These additional disks, rollers, andactuators are omitted from the drawings for clarity.

The variator fault detection system 126 may be used with other variatorimplementations, as well. Alternative embodiments of the variator 24 mayinclude a lesser or greater number of disks, rollers, and/or actuators.In one such embodiment, one hydraulic actuator is used to control all ofthe rollers. In another embodiment, a compact lever arrangement is usedin place of the inline piston design shown in FIG. 1B. Moreover, someembodiments may use a partially toroidal rather than a full toroidalconfiguration.

The variator 24 and the clutches 26 of the transmission 12 arecontrolled by an electro-hydraulic control system 14. Theelectro-hydraulic control system 14 has a variator control circuit 28and a clutch control circuit 30. In general, the linkages 38, 40, 42represent hydraulic fluid connections between components of the variator24 and the variator control circuit 28, between the clutch or clutches26 and the clutch control circuit 30, and between the variator controlcircuit 28 and the clutch control circuit 30.

The variator control circuit 28 controls the variator ratio. Aspects ofthe variator control circuit 28 are described below with reference toFIGS. 2-6. The clutch control circuit 30 controls the application andrelease of the clutches 26. Aspects of the clutch control circuit 30 arethe subject of U.S. Provisional Patent Application Ser. No. 61/287,031,filed Dec. 16, 2009, and U.S. Provisional Patent Application Ser. No.61/287,038, filed Dec. 16, 2009, both of which are incorporated hereinby this reference in their entirety.

The operation of the electro-hydraulic control system 14 is controlledby an electronic control unit 16. The linkages 44, 46 are used toschematically represent electrical connections between the electroniccontrol unit 16 and the electro-hydraulic control circuits 28, 30 of theelectro-hydraulic control system 14, as will be understood by thoseskilled in the art. The linkages 44, 46 may include insulated wiring,wireless links, or other suitable connections for exchanging data,communications and computer instructions. The electronic control unit 16may be implemented as multiple separate logical or physical structuresor as a single unit. For example, the electronic control unit 16 maycontrol aspects of the operation of the drive unit 10 in addition to thetransmission 12, or the electronic control unit may comprise a number ofmodules that control different aspects of the operation of the driveunit 10 and/or transmission 12.

The electronic control unit 16 includes computer circuitry configured tocontrol the operation of the transmission 12 based on inputs fromvarious components of the transmission 12 and, in some embodiments, fromthe drive unit 10. Such inputs may include digital and/or analog signalsreceived from sensors, controls or other like devices associated withthe vehicle components. The electronic control unit 16 processes inputsand parameters and issues electrical control signals to variouscomponents of the electro-hydraulic control system 14.

For example, the electronic control unit 16 monitors the status ofvalves in the electro-hydraulic control system 14. Sensing devices suchas pressure switches or the like detect changes in valve positionswithin the electro-hydraulic control system 14 and send electricalsignals to the electronic control unit 16 to indicate detected changes.The electronic control unit 16 executes computerized logic andinstructions to determine, based on the signals received from thesensing devices, whether a fault has occurred in any of the componentsof the electro-hydraulic control system 14.

The variator fault detection system 126 is incorporated into thevariator control circuit 28. The variator control circuit 28 applies acontrolled force to the variator rollers by adjusting the pressures inthe hydraulic actuators 35. As shown schematically in FIG. 2, each ofthe hydraulic actuators 35 includes a pair of opposing faces 70, 72,which are movable within their respective cylinders 74, 76. Each of theopposing faces 70, 72 is exposed to hydraulic fluid pressure so that theforce applied by the actuator 35 to its respective roller is determinedby the difference in the two pressures. Accordingly, the force appliedby the actuators 35 to the rollers has both a magnitude and a direction.For example, the direction of the force may be considered positive ifthe face 70 receives greater pressure than the face 72 and negative ifthe face 72 receives greater pressure than the face 70, or vice versa.Illustratively, each of the hydraulic actuators 35 includes adouble-acting piston and cylinder arrangement.

The pressure applied to one side (e.g., the face 70) of the actuator 35is commonly referred to as “S1,” while the pressure applied to the otherside (e.g., the face 72) of the actuator 35 is commonly referred to as“S2.” The difference between the S1 and S2 pressures determines theforce applied by the actuators 35 to their respective rollers.

The actuators 35 and the fluid lines S1, S2 are configured to ensurethat the actuators 35 all react the same way, so that all of the rollers25 of the variator 24 are continuously maintained at the same pressuredifferential. A “higher pressure wins” valve 78 connects whichever ofthe two lines S1, S2 is at a higher pressure to an end load arrangement80.

The variator control circuit 28 adjusts the pressures in the lines S1,S2. A source of hydraulic fluid (i.e., a sump) 68 supplies fluid to apump 66. Electronically-controlled valves 60, 62, 64 regulate the fluidpressure that is applied to the lines S1 and S2. The valve 64 is a typeof pressure control valve commonly referred to as a main modulatorvalve. The main modulator valve 64 modulates the fluid pressureaccording to a predetermined desired pressure level for the variatorcontrol circuit 28.

The valves 60, 62 are trim valves, each of which includes avariable-bleed solenoid or similar device that outputs a variable fluidpressure in response to signals from the electronic control unit 16. Thetrim valve 60 is fluidly coupled to a shift valve 50 by a fluid passage120, and the trim valve 62 is fluidly coupled to a shift valve 52 by afluid passage 122. The trim valve 60 controls the application of fluidpressure to the line S1 through the shift valve 50, and the trim valve62 controls the application of fluid pressure to the line S2 through theshift valve 52.

The variator fault detection system 126 includes a variator lockoutvalve system 116. In the variator lockout valve system 116, the positionof the shift valve 50 determines whether or not the trim valve 60supplies fluid pressure to the line S1, and the position of the shiftvalve 52 determines whether or not the trim valve 62 supplies fluidpressure to the line S2. The trim valve 60 is in fluid communicationwith the line S1 when the shift valve 50 is destroked, as shown in FIGS.3, 5 and 6 described below. The trim valve 62 is in fluid communicationwith the line S2 when the shift valve 52 is destroked, as shown in FIGS.3, 4, and 6 described below.

The variator lockout valve system 116 includes a trim valve 112 and ashift valve 114. The trim valve 112 is fluidly coupled to the shiftvalves 50, 52 by a passage 124. The trim valve 112 may be used to supplyfluid pressure to the line S1 in the event that the trim valve 60 fails,and the trim valve 112 may be used to supply fluid pressure to the lineS2 in the event that the trim valve 62 fails.

Aspects of the variator lockout valve system 116, including the trimvalve substitution scheme, are described in U.S. Provisional PatentApplication Ser. No. 61/286,974, filed Dec. 16, 2009, which isincorporated herein by this reference in its entirety.

The variator fault detection system 126 also includes a fast valveactuation system 48, which is coupled between the trim valves 60, 62 andthe rest of the variator control circuit 28. The fast valve actuationsystem 48 has its own fluid circuit 56, which is coupled to a fluidsupply 54. The fluid circuit 56 includes a pair of passages 90, 92,which fluidly couple the respective valve heads and spring pockets ofthe shift valves 50, 52 to one another as best shown in FIGS. 3-6.

In the variator fault detection system 126, the arrangement of thepassages 90, 92 of the fast valve actuation system 48 prevents a statein which both of the shift valves 50, 52 are stroked at the same time.The fluid passage 90 couples the output passage 156 of theelectro-hydraulic actuator 108 to valve head 82 of the shift valve 50and the spring pocket 88 of the shift valve 52. The fluid passage 92couples the output passage 158 of the electro-hydraulic actuator 110 tothe valve head 84 of the shift valve 52 and the spring pocket 86 of theshift valve 50.

In operation, when the electro-hydraulic actuator 108 is actuated (FIG.4), fluid pressure is output to the valve head 82 of the shift valve 50and to the spring pocket 88 of the shift valve 52 at the same time, orat nearly the same time. Likewise, when the electro-hydraulic actuator110 is actuated (FIG. 5), fluid pressure is output to the valve head 84of the shift valve 52 and to the spring pocket 86 of the shift valve 50at the same time, or at nearly the same time.

If both of the electro-hydraulic actuators 108, 110 are actuated at thesame time (e.g., if one of the electro-hydraulic actuators 108, 110 isactuated, or remains actuated, in error) the fluid pressure directed tothe spring pockets 86, 88 via the fluid passages 90, 92 prevents theshift valves 50, 52 from both stroking at the same time, resulting in avalve state that looks similar to FIG. 3. Each one of the shift valves50, 52 can only be stroked if the electro-hydraulic actuator 108, 110coupled to the other of the shift valves 50, 52 is not actuated.

Thus, the shift valves 50, 52 have three possible states: a “00” statein which both of the shift valves 50, 52 are destroked, a “10” state inwhich the shift valve 50 is stroked and the shift valve 52 is preventedfrom stroking, and a “01” state in which the shift valve 50 is preventedfrom stroking and the shift valve 52 is stroked.

Further aspects of the fast valve actuation system 48 are described inU.S. Provisional Patent Application Ser. No. 61/287,003, filed Dec. 16,2009, which is incorporated herein by this reference in its entirety.

FIGS. 3-6 illustrate possible states of the variator fault detectionsystem 126. FIG. 3 illustrates a normal operating mode in which novariator faults are detected. FIG. 4 illustrates a valve state in whicha fault may have occurred at the shift valve 50. FIG. 5 illustrates avalve state in which a fault may have occurred at the shift valve 52.FIG. 6 illustrates a valve state in which a variator fault (variatorpressure too high) is detected.

Each of the shift valves 50, 52 resides in a valve chamber of a valvebody of the electro-hydraulic control system 14. The shift valves 50, 52are axially movable between destroked and stroked positions in theirrespective valve chambers. The valve chambers are omitted from thedrawings for clarity.

The shift valve 50 selectively directs fluid pressure to the fluidpassage S1 of a torque transferring mechanism 140 of the automatictransmission. The shift valve 52 selectively directs fluid pressure tothe fluid passage S2 of a torque transferring mechanism 142 of thetransmission 12. The torque transferring mechanisms 140, 142 arevariator disk actuators, in accordance with the particular design of thetransmission 12. As illustrated, the torque transferring mechanisms 140,142 are opposing sides of the hydraulic piston/cylinder arrangementdescribed above.

The shift valve 50 includes a valve head 82, a spring pocket 86, and anumber of axially-spaced lands 144, 146, 148 therebetween. The lands144, 146, 148 define a pair of ports 94, 96. The spring pocket 86contains a return spring 164, which biases the shift valve 50 in thedestroked position shown in FIGS. 3, 5 and 6.

Similarly, the shift valve 52 includes a valve head 84, a spring pocket88, and a number of axially-spaced lands 150, 152, 154 therebetween. Thelands 150, 152, 154 define a pair of ports 98, 100. The spring pocket 88contains a return spring 166, which biases the shift valve 52 in thedestroked position shown in FIGS. 3, 4, and 6.

The shift valve 50 is fluidly coupled to an electro-hydraulic actuator108 by an output passage 156. A source of pressurized hydraulic fluid 54feeds fluid pressure to the electro-hydraulic actuator 108 through afluid passage 160. The electro-hydraulic actuator 108 selectivelyoutputs the fluid pressure to either the output passage 156 or to anexhaust chamber 106, in response to electrical signals issued by theelectronic control unit 16.

In the illustrations, the electro-hydraulic actuator 108 is anormally-low, on-off solenoid valve. When the electro-hydraulic actuator108 receives electrical input (i.e. current or voltage) from theelectronic control unit 16 (i.e., the electro-hydraulic actuator 108 is“actuated”), the electro-hydraulic actuator 108 outputs fluid pressurefrom the passage 160 to the output passage 156. In the absence ofelectrical input, the electro-hydraulic actuator 108 directs fluidpressure from the passage 160 to the exhaust chamber 106. When theelectro-hydraulic actuator 108 is actuated, fluid pressure applied tothe valve head 82 via the output passage 156 strokes the shift valve 50as shown in FIG. 4.

In similar fashion to the shift valve 50, the shift valve 52 is fluidlycoupled to an electro-hydraulic actuator 110 by an output passage 158.The source of pressurized hydraulic fluid 54 feeds fluid pressure to theelectro-hydraulic actuator 110 through the fluid passage 160. Theelectro-hydraulic actuator 110 selectively outputs fluid pressure toeither the output passage 158 or to an exhaust chamber 106, in responseto electrical signals issued by the electronic control unit 16.

In the illustrations, the electro-hydraulic actuator 110 is anormally-low, on-off solenoid valve. When the electro-hydraulic actuator110 receives electrical input from the electronic control unit 16 (i.e.,the electro-hydraulic actuator 110 is “actuated”), the electro-hydraulicactuator 110 outputs fluid pressure from the passage 160 to the outputpassage 158. In the absence of electrical input, the electro-hydraulicactuator 110 directs fluid pressure from the passage 160 to an exhaustchamber 106. When the electro-hydraulic actuator 110 is actuated, fluidpressure applied to the valve head 84 via the output passage 158 strokesthe shift valve 52 as shown in FIG. 5.

As shown in FIGS. 3-6, the port 94 of the shift valve 50 is in fluidcommunication with the fluid passage S1 of the torque transferringmechanism 140 both when the shift valve 50 is destroked and when theshift valve 50 is stroked. Similarly, the port 98 of the shift valve 52is in fluid communication with the fluid passage S2 of the torquetransferring mechanism 142 both when the shift valve 52 is destroked andwhen the shift valve 52 is stroked.

The trim systems 60, 62, and 112 are selectively in fluid communicationwith the fluid passages S1, S2, depending upon the position of the shiftvalves 50, 52. The trim system 60 is configured to control theapplication of fluid pressure to the fluid passage S1 when the shiftvalve 50 is destroked. The trim system 62 is configured to control theapplication of fluid pressure to the fluid passage S2 when the shiftvalve 52 is destroked.

When the shift valve 50 is stroked, the port 94 is disconnected from thetrim system 60, as shown in FIG. 4. Similarly, when the shift valve 52is stroked, the port 98 is disconnected from the trim system 62, asshown in FIG. 5. The trim system 112 is connected to the fluid passageS1 through the port 94 of the shift valve 50 when the shift valve 50 isstroked. The trim system 112 is connected to the fluid passage S2through the port 98 of the shift valve 52 when the shift valve 52 isstroked.

In the variator fault detection system 126, a pair of sensing devices(e.g. pressure switches) are used to monitor the status of the shiftvalves 50, 52, detect faults occurring in the shift valves 50, 52 detectfailures in the trim valves 60, 62 causing the variator pressure to betoo high, or in the trim valves 60, 62, and report faults detected by avariator fault valve 118 to the electronic control unit 16. The ports96, 100 of the shift valves 50, 52, are in fluid communication withpressure switches 102, 104, respectively, and with the variator faultvalve 118.

The port 96 (and thus, the pressure switch 102) is pressurized when theshift valve 50 is stroked or when the shift valve 50 is destroked andthe variator fault valve 118 is destroked. The port 100 (and thus, thepressure switch 104) is pressurized when the shift valve 52 is strokedor when the shift valve 52 is destroked and the variator fault valve 118is destroked. The variator fault valve 118 is a two-position valve thatis normally stroked, but it destrokes if the variator pressure output tothe end load arrangement 80 is too high, i.e., is higher than the trimpressure input to the variator on lines S1, S2. When pressurized, thepressure switches 102, 104 send electrical signals to the electroniccontrol unit 16.

As described above, there are instances during normal operation of thetransmission 12 in which one or the other of the shift valves 50, 52 isstroked and the corresponding pressure switch 102, 104 is actuated.Accordingly, the electronic control unit 16 uses other information incombination with the signals generated by the pressure switches 102,104, to determine whether a fault has occurred in one of the valves 50,52, 60, 62.

The pressure switches 102, 104 are used to determine whether one of theshift valves 50, 52 may be stuck in the wrong position. FIG. 4 shows aconfiguration of the variator fault detection system 126 that mayindicate a faulty shift valve 50. The shift valve 50 is stroked,actuating the pressure switch 102. The land 154 of the shift valve 52 isconfigured to allow enough fluid flow through the passage 160 to thechamber 96 to change the state of the pressure switch 102. Commonlyreferred to as a “tombstone,” the land 154 may have an annulus on itstop and bottom portions, to relieve pressure around the valve, balancingpressure (i.e. preventing side loads) or for other reasons.

To determine whether or not the shift valve 50 is operating normally,the electronic control unit 16 determines whether the electro-hydraulicactuator 108 is actuated or deactuated (i.e. on or off). If theelectro-hydraulic actuator 108 is off, but the pressure switch 102 isactuated, then the electronic control unit 16 may determine that theshift valve 50 is stuck in the stroked position. Likewise, if theelectro-hydraulic actuator 108 is on but the pressure switch 102 is notactuated, then the electronic control unit 16 may determine that theshift valve 50 is stuck in the destroked position.

Similarly, FIG. 5 shows a configuration of the variator fault detectionsystem 126 that may indicate a faulty shift valve 52. The shift valve 52is stroked, actuating the pressure switch 104. To determine whether ornot the shift valve 52 is operating normally, the electronic controlunit 16 determines whether the electro-hydraulic actuator 110 isactuated or deactuated (i.e. on or off). If the electro-hydraulicactuator 110 is off, but the pressure switch 104 is actuated, then theelectronic control unit 16 may determine that the shift valve 52 isstuck in the stroked position. Likewise, if the electro-hydraulicactuator 110 is on but the pressure switch 104 is not actuated, then theelectronic control unit 16 may determine that the shift valve 52 isstuck in the destroked position.

FIG. 6 shows a configuration of the variator fault detection system 126in which a variator fault is detected by the variator fault valve 118.If a variator fault (i.e. a malfunction that causes the variatorpressure to be too high) occurs, the variator fault valve 118 destrokes.

When both of the shift valves 50, 52 are destroked, both of theelectro-hydraulic actuators 108, 110 are deactuated (i.e., off). In thisscenario, destroking of the variator fault valve 118 couples the passage128 to both of the ports 96, 100, and both of the pressure switches 102,104 are actuated by fluid pressure supplied by the pressure source 54through the variator fault valve 118. Thus, the “11” state indicatesthat both of the pressure switches 102, 104 are actuated, not that theshift valves 50, 52 are both stroked. This is possible because thepassages 90, 92 prevent the shift valves 50, 52 from attaining the “11”state (i.e. a state in which both of the shift valves are stroked at thesame time).

The “11” state is also used by the pressure switches 102, 104 incombination with the variator fault valve 118 and other information todetermine whether one of the trim valves 60, 62 has failed causing thevariator pressure to be too high. If the shift valve 50 is stroked whena variator fault occurs, the pressure switch 102 is actuated by fluidpressure via the passage 160 as shown in FIG. 4. If the variator faultvalve 118 detects high variator pressure at the same time as the shiftvalve 50 is stroked, only the pressure switch 104 is pressurized by theoutput of the variator fault valve 118 through the passage 128, becausethe passage 128 to the shift valve 50 is blocked by the land 146 whenthe shift valve 50 is stroked. Nonetheless, both of the pressureswitches 102, 104 are actuated, indicating a variator fault.

In this scenario, the electronic control unit 16 determines that theelectro-hydraulic actuator 108 is actuated. This information, incombination with the “11” state of the pressure switches 102, 104,indicates that a failure has occurred at the trim valve 62. This is sobecause when the shift valve 50 is stroked, the trim valve 60 is blocked(i.e., not outputting fluid pressure to the variator line S1) as shownin FIG. 4 and described above.

Similarly, if the shift valve 52 is stroked when a variator faultoccurs, the pressure switch 104 is actuated by fluid pressure via thepassage 160 as shown in FIG. 5. If the variator fault valve 118 detectshigh variator pressure at the same time as the shift valve 52 isstroked, only the pressure switch 102 is pressurized through the passage128, because the passage 128 to the shift valve 52 is blocked by theland 152 when the shift valve 52 is stroked. Nonetheless, both of thepressure switches 102, 104 are actuated, indicating a variator fault.

In this scenario, the electronic control unit 16 determines that theelectro-hydraulic actuator 110 is actuated. This information, incombination with the “11” state of the pressure switches 102, 104,indicates that a failure has occurred at the trim valve 60. This is sobecause when the shift valve 52 is stroked, the trim valve 62 is blocked(i.e. not outputting fluid pressure to the variator line S2) as shown inFIG. 5 and described above.

Table 1 below summarizes fault conditions detected by the pressureswitches 102, 104, as described in this disclosure, where “0” denotes adestroked, off, or deactuated state and “1” denotes a stroked, on, oractuated state.

TABLE 1 Pressure Pressure Variator Switch Switch Actuator Fault Locationof 102 104 Actuator 108 110 Valve 118 Fault 0 0 0 0 0 Variator 1 0 0 0 1Shift Valve 50 1 0 1 1 1 Shift Valve 52 1 1 1 0 0 Trim Valve 62 0 1 0 01 Shift Valve 52 0 1 1 1 1 Shift Valve 50* 1 1 0 1 0 Trim Valve 60

The asterisk (*) in row 6 of Table 1 is used to denote a state that, inthe illustrated embodiment, may be commanded (erroneously, perhaps), butnot achieved. That is, actuating both of the actuators 108, 110 will notcause both of the shift valves 50, 52 to be stroked, because theconfiguration of the shift valves 50, 52 prevents simultaneous stroking,as described above.

If any of the above-described faults occurs, the backup trim system 112is implemented to enable the vehicle to “limp home” as described in theaforementioned U.S. Provisional Patent Application Serial No.61/286,974.

The present disclosure describes patentable subject matter withreference to certain illustrative embodiments. The drawings are providedto facilitate understanding of the disclosure, and may depict a limitednumber of elements for ease of explanation. Except as may be otherwisenoted in this disclosure, no limits on the scope of patentable subjectmatter are intended to be implied by the drawings. Variations,alternatives, and modifications to the illustrated embodiments may beincluded in the scope of protection available for the patentable subjectmatter.

1. A variator control circuit, comprising: a plurality of variatorcontrol devices in fluid communication with a variator of a continuouslyvariable transmission, and a maximum of two sensing devices configuredto detect faults occurring in any one of the plurality of variatorcontrol devices.
 2. The variator control circuit of claim 1, wherein theplurality of variator control devices comprises a pair of shift valvesand a plurality of trim valves, each of the shift valves has a firstport and a second port axially spaced from the first port, each of thetrim valves is selectively coupled to the first port of one of the shiftvalves, and each of the sensing devices is coupled to the second port ofone of the shift valves.
 3. The variator control circuit of claim 2,comprising a variator fault valve selectively coupled to the second portof each of the shift valves.
 4. The variator control circuit of claim 2,wherein each of the shift valves has a valve head and a spring pocket,comprising a first passage fluidly coupling the valve head of one of theshift valves to the spring pocket of the other shift valve and a secondpassage fluidly coupling the valve head of the other shift valve to thespring pocket of the one shift valve.
 5. The variator control circuit ofclaim 2, wherein the plurality of variator control devices comprises anelectro-hydraulic actuator coupled to one of the shift valves.
 6. Thevariator control circuit of claim 3, wherein the variator fault valvehas a first position and a second position axially spaced from the firstposition, and wherein the variator fault valve outputs fluid pressure tothe second port of at least one of the pair of shift valves when thevariator fault valve is in the second position.
 7. The variator controlcircuit of claim 6, wherein each of the shift valves has a firstposition and a second position axially spaced from the first position,and wherein the variator fault valve only outputs fluid pressure to thesecond port of one of the shift valves when the one shift valve is inthe first position and the variator fault valve is in the secondposition.
 8. The variator control circuit of claim 7, wherein thevariator fault valve only outputs fluid pressure to the second port ofthe other of the shift valves when the other shift valve is in the firstposition and the variator fault valve is in the second position.
 9. Thevariator control circuit of claim 8, wherein (i) the plurality of trimvalves comprises a first trim valve and a second trim valve, (ii) thefirst trim valve is fluidly coupled to the first port of one of theshift valves when the one shift valve is in the first position, and(iii) the first position of the one shift valve is a destroked positionand the second position of the one shift valve is a stroked position.10. The variator control circuit of claim 9, wherein (i) the second trimvalve is fluidly coupled to the first port of the other of the shiftvalves when the other shift valve is in the first position, (ii) thefirst position of the other shift valve is a destroked position and thesecond position of the other shift valve is a stroked position, and(iii) the second trim valve is disconnected from the first port of theother shift valve when the other shift valve is in the stroked position.11. A variator control circuit comprising: a plurality of variatorcontrol devices in fluid communication with a variator of a continuouslyvariable transmission, including: (i) a first shift valve and a secondshift valve, each of the shift valves movable from a first position to asecond position axially spaced from the first position; (ii) a firsttrim valve selectively coupled to the first shift valve and a secondtrim valve selectively coupled to the second shift valve; and (iii) afirst electro-hydraulic actuator coupled to the first shift valve and asecond electro-hydraulic actuator coupled to the second shift valve, anda plurality of sensing devices configured to detect faults occurring inany one of the plurality of variator control devices, including: (i) afirst sensor coupled to the first shift valve, and (ii) a second sensorcoupled to the second shift valve.
 12. The variator control circuit ofclaim 11, wherein each of the shift valves has a first port and a secondport axially spaced from the first port, and wherein the first trimvalve is selectively coupled to the first port of the first shift valveand the second trim valve is selectively coupled to the first port ofthe second shift valve.
 13. The variator control circuit of claim 12,wherein the first sensor is coupled to the second port of the firstshift valve and the second sensor is coupled to the second port of thesecond shift valve.
 14. The variator control circuit of claim 13,comprising a variator fault valve selectively coupled to the second portof the first shift valve and selectively coupled to the second port ofthe second shift valve.
 15. The variator control circuit of claim 14,wherein the variator fault valve has a first position and a secondposition axially spaced from the first position, and wherein thevariator fault valve outputs fluid pressure to at least one of thesecond port of the first shift valve and the second port of the secondshift valve when the variator fault valve is in the second position. 16.A variator control circuit comprising: a plurality of variator controldevices in fluid communication with a variator of a continuouslyvariable transmission, including: (i) a first shift valve in fluidcommunication with a second shift valve, each of the shift valves influid communication with a variator of a continuously variabletransmission, movable from a first position to a second position axiallyspaced from the first position, and having a valve head and a springpocket, (ii) a first trim valve selectively coupled to the first shiftvalve and a second trim valve selectively coupled to the second shiftvalve, (iii) a first electro-hydraulic actuator coupled to the firstshift valve and a second electro-hydraulic actuator coupled to thesecond shift valve, and (iv) a variator fault valve selectively coupledto the first shift valve and selectively coupled to the second shiftvalve; and a plurality of sensing devices configured to detect faultsoccurring in any one of the plurality of variator control devices,including (i) a first sensor coupled to the first shift valve, and (ii)a second sensor coupled to the second shift valve.
 17. The variatorcontrol circuit of claim 16, wherein (i) each of the shift valves has afirst port and a second port, (ii) the first port of each of the shiftvalves is in fluid communication with the variator, (iii) the first trimvalve is fluidly coupled to the first port of the first shift valve whenthe first shift valve is in the first position, and (iv) the second trimvalve is fluidly coupled to the first port of the second shift valvewhen the second shift valve is in the first position.
 18. The variatorcontrol circuit of claim 17, wherein the first sensor is coupled to thesecond port of the first shift valve and the second sensor is coupled tothe second port of the second shift valve.
 19. The variator controlcircuit of claim 18, wherein the variator fault valve is selectivelycoupled to the second port of the first shift valve and selectivelycoupled to the second port of the second shift valve.
 20. The variatorcontrol circuit of claim 19, wherein each of the shift valves has avalve head and a spring pocket, comprising a first passage fluidlycoupling the valve head of the first shift valve to the spring pocket ofthe second shift valve and a second passage fluidly coupling the valvehead of the second shift valve to the spring pocket of the first shiftvalve.